Gas exhaust silencer

ABSTRACT

An air exhaust silencer comprises a housing having an air inlet and an air outlet defined by baffle members made of a porous material; a sound absorbing material is disposed in the housing between the baffle members; the air enters through the inlet port and is broken up by the porous inlet baffle for distribution through the sound absorbing material and exhaust through the porous outlet baffle at which the air flow is further broken up to thereby considerably reduce the noise level of the exhausted air passing through the silencer.

United States Patent Blatt et al.

[4 June 27, 1972 [54] GAS EXHAUST SILENCER [72] Inventors: LelandFrancis Blatt; Frank H. Wlesenhoier, both of 31915 Groesbeck Highway,Fraser, Mich. 48026 [22] Filed: Oct. 15, 1970 [21] Appl. No 81,051

[52] U.S.Cl ..l81/50,181/57, 181/60,

[51] lnt.Cl ..F01n 1/10,F01n 7/16 [58] Field ofSearch..l81/42,47,47,1,50, 56, 57, 181/60, 71, 63, 68-70 {56] References CitedUNITED STATES PATENTS 2,499,018 2/1950 Christiano et a1 ..l8l/503,115,209 12/1963 Bembinster ..181/50 3,163,256 12/1964 Lanning..l8l/71X 3,270,834 9/1966 Bratt .Q ..181/60 X 1,839,192 1/1932 Baits,....181/57 X 2,019,746 11/1935 Tatter ..181/50 X 3,381,774 5/1968 Stadeet al.. ..l8l/57 X 2,392,559 1/1946 Varma ..181/50 PrimaryExaminer-Robert S. Ward, .Ir. AttorneyCullen, Settle, Sloman & Cantor[57] ABSTRACT An air exhaust silencer comprises a housing having an airinlet and an air outlet defined by baffle members made of a porousmaterial; a sound absorbing material is disposed in the housing betweenthe baflIe members; the air enters through the inlet port and is brokenup by the porous inlet baffle for distribution through the soundabsorbing material and exhaust through the porous outlet baffle at whichthe air flow is further broken up to thereby considerably reduce thenoise level of the exhausted air passing through the silencer.

7 Claims, 4 Drawing Figures PA'TENTEnJunzjmz 3.672.465 sum 10F 2 INV ENTORS I LELAbD FRANCIS BLATT FRANKMWIESENHOFER 13v WM, {6x22 ATTORNEYSPATENTEDJum I972 3. 672.465

sum 2 or 2 FIG?) INVENTORS LELAND FRANCIS BLATT FRANK ILWIESENHOFERATTORNEYS GAS EXHAUST SILENCER BACKGROUND AND SUMMARY OF THE INVENTIONThe present invention relates to sound absorbing devices and more inparticular to a noise subduing device to maintain a specific noise levelwithin acceptable limits.

Almost universally, every thing, substance or matter moving provides orproduces noise at varying frequencies and at different noise levelswhich may range from a low frequency whisper to high frequency squeals.

Any consistent sound at whatever noise level is, in most cases, annoyingto the human ear, although the sound level may not be as high as toproduce a health hazard. However, in connection with machinery, whetherit be mechanical, electrical or fluid power operated or by combustion,noises are produced which, in instances, exceed a safe level,particularly at high frequencies.

It is known in the industry that the federal government establishedindustrial safety standards by the provision of the Walsh-Healey Actwhich was amended on May 8, 1969, in regard to occupational noiseexposure, setting a standard providing that a person may not workmorethan 8 hours at a maximum 90 dBA (90 decibels measured on the A-scale ofa sound level meter).

Many noises produced in a plant or similar working place, areconsiderably on a higher scale than 90 dBA Most of these noises are notmerely pure tones, but in most cases are a combination of sounds and mayrange from a low frequency roar to a high frequency squeal. Obviously,combined frequencies require differentiating of materialsinside thedevice to stop or absorb those frequencies or separate those frequenciesin order that they not be added or combined with one another to producea sound level unacceptable or unhealthful to human beings. Anotherfactor to be considered is the power level of the sound field. Thus, ifa great deal of noise is being produced at different frequencies, or thelevel of power is high, it would require extremely large and complicatedsilencers to reduce the noise to within a tolerance acceptable to ahuman being at a certain distance from the origin of the sound.

As mentioned before, sound is produced by matters or substances flowingor moving through the air or through another substance and the noiselevel of the sound is dependent on the pressure and speed of movement ofthe moving substance and the relative resistance of the matter or othersubstance through which the moving substance moves. Thus, air flowingthrough the orifice or venturi of an exhaust valve at relatively highspeed and pressure, creates a high frequency squealing sound, whereas,for instance, the sound produced inside of air operated tools is muchmore subdued, but this sound is combined with the noise created by theworking parts of the tool. Thus, these two examples require differenttypes of sound absorbing material for effective silencing to within asafe level.

Considerable difficulties are experienced in moderating or absorbingthese sounds created by the exhaust of pneumatic valves, motors andother air operated tools in the industry. Noise is also produced by thesound of mechanical movement of the working parts of the tools coupledwith other frequencies caused by air vibrations as air travels through aparticular valve or pneumatic motor.

It is known to the men skilled in the art of noise reduction orabsorbtion that, when the daily noise exposure is comprised of two ormore periods of noise, the different level and combined effect should beconsidered rather than the individual effect of each.

In most air tool and/or air valve applications, where a great deal ofair flow is present, requires the design of silencer chambers to be ofutmost consideration so as not to creat excessive back pressure withinthe tool or valve which will cause a slow-down in the cycle of theoperation time.

Accordingly, the present invention provides an improved air exhaustsilencer construction adapted to effectively reduce high noise levels toa safe level not exceeding 90dBA.

The present improved construction comprises a housing which has an inletconnected to the air exhaust conduit and which is filled with a soundabsorbing material of a known substance which is retained at both endsof the housing between baffle members made from porous material. One ofthe bafile members which are axially located in the housing defines ahigh noise air inlet and the other bafile member defines a low noiseexit to the atmosphere.

Thus, the exhausted air from the respective noise producinG apparatusenters the housing through the inlet and impinges against the firstporous baffle member which acts to minutely breakup the air stream fordistribution through the intermediate sound absOrbing material and finalexit through the second porous baffle member at a considerably reducednoise level.

The present invention will be best understood by reference to thefollowing detailed description with particular reference to the attacheddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings illustrate apreferred embodiment of the improved silencer structure in which:

FIG. 1 is a longitudinal cross-section through the present improvedsilencer structure;

FIG. 2 is a transverse cross-section through the structure of FIG. 1 asseen along line 2-2 thereof;

FIG. 3 is a longitudinal cross-section through a modified silencersimilar to FIG. 1 constructed in accordance with the present invention;and v FIG. 4 is a detached detail view of the alternate end bafflemember employed in the modification of FIG 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to the attacheddrawings and particularly FIGS. 1 and 2, the present improved airexhaust silencer structure comprises a housing generally indicated at 10which, at one end, is attached to an exhaust pipe or conduit 12 havingconnection to a noise producing device (not shown).

The silencer housing 10 may be of generally cylindrical or barrel likestructure comprising an open-ended tubular member 14 which may be ofsuitable heat resistant material as generally employed in silencerstructures of this kind. One end of the cylindrical member 14 is closedby a front end cap 16 which has a threaded bore 18 for attachment to theair exhaust pipe 12 and which defines the inlet into the silencer.

Inwardly of the cylindrical member 14 and directly adjacent the end cap16 a baffle member 20 is provided composed of a radial flange portion 22which is clamped between the end cap 16 and a radial shoulder 15 of thecylindrical member 14 to securely retain the bafile member within thehousing. The baffle member 20 is formed into a frustoconical section 24which axially inwardly extends through the cylindrical member 14 asubstantial distance, having an inner closed end 26. The frustoconicalportion 24 of the baffle member 20 is in axial alignment with the inlet18 to form an expansion chamber 28. The frustoconical portion 24 is ofsufficient length to provide a sufficiently large internal surface area30 for impingement of the exhaust air thereon and has a sufficientchamber area to accommodate free expansion of the exhaust air enteringthe chamber 28 frorninlet 18.

The baffle member 20 is made of a gas permeable material which may beheat resistant and having a high porosity such as sintered bronze or thelike, to permit the expanded air to enter the cylindrical chamber 17from the expansion chamber 28 through the porous walls of the truncatedcone section 24.

The cylindrical chamber 17 of the cylindrical member 14 is filled with asound absorbing material 32 of any known suitable material compositionusually employed in silencer applications of this kind, which mayinclude porous urethane, sponge rubber, felt, steel wool, coiledscreening and the like. All of these materials have different effects inabsOrbing sound at various frequencies.

The opposite exit end of the cylindrical member 14 is closed by anotherbaffle member 34, which comprises a substantially solid plate supportedwithin a radial recess 36 provided in the cylindrical member 14, andretained in position by means of a lock ring 38.

The plate like baffle member 34 is likewise composed of a gas permeablematerial having a high porosity, such as for instance sintered bronze,to permit exit of the muffled air from the chamber 17 to the atmosphere.

In operation: exhausted air, which may be hot in the case of combustiongas exhaust, enters the silencer structure through the conduit 12 andinlet 18 for entrance into the expansion chamber 28 of the frustoconicalportion 24 of the first baffle member 20. The exhausted air is expandedin chamber 28 and impinges radially and axially against the internalsurface 30 thereof for penetration through the porous walls of the firstbaffle member 20 into the chamber 17 'of the cylindrical member 14 topenetrate through the sound absorbing material 32, as indicated by theflow arrows.

The initial sound level of the exhausted air, as it enters the expansionchamber 28, is first considerably reduced by being minutely broken up asthe air penetrates through the porous walls of the first baffle memberinto the main chamber of the silencer. During penetration of the airthrough the sound absorbing material 32, the sound level is furtherreduced to a still lower value.

The air then travels through the sound absorbing material 32 towards therear of the silencer for impingement upon the second, plate like bafflemember 34 and penetration therethrough to the atmosphere. The plate likeexit baffle member 34 further breaks up the air fiow as it penetratesthrough the porous structure of the baffle member to thereby stillfurther reduce the noise level as the air exits to the atmosphere.

With reference now to FIGS. 3 and 4, the embodiment is substantiallysimilar to the embodiment in FIGS. I and 2 and similar parts areidentified by the same reference numerals.

In the silencer of FIGS. 3 and 4, the second outlet baffle member 34 hasbeen replaced by a perforated plate 40 which, as seen in FIG. 4, isprovided with a plurality of holes or apertures 42. The perforated plate40 is preferably made of aluminum and the sound absorbing material 32 inthis instance is preferably an open cellurethane. g

This silencer construction is particularly applicable for installationon air venturies which run on lowPSI but normally create soundsofannoying frequencies.

The improved silencers of the present invention as disclosed herein, areparticularly applicable to absorb sounds created by air flowing from apipe such as through an exhaust valve and, depending on the selection ofsuitable material, to reduce other noises such as produced by air tools,combustion engines or the like.

It will be understood that for any particular application, the sinteredbronze used must be of suitable density to provide a specified pressuredrop per square inch for 1 cubic foot air passage per square inch,which, of course, varies with the individual application.

Thus, the present invention provides an improved, highly effective, airexhaust silencer of relatively simple structure which meets therequirements of the recently amended Walsh- Healey Act concerningoccupational noise exposure and which specifies a maximum noise level of90 decibels during any 8 hour period.

The present improved silencer is constructed to reduce the noise levelof exhausted air, and particularly industrial air exhaust, to well belowthe required value by the provision of oppositely disposed, porous, gaspermeable baffle members at both ends of an intermediate sound absorbingmedia to obtain multiple noise level reduction as the exhausted airtravels through the silencer.

It will be appreciated that in some applications where moist air ispresent expanding through orifices at a very high rate,

the exhausting ai r ma take on so much heat that the silencer attachedto the air ou et will freeze solid. In these types of applications,additional units may have to be applied or, conversely, the silencerunit will have to be attached as close as possible to the air motor topermit the frictional heat of the working parts to be transmitted intothe silencer to keep the cooling effect above the freezing point.

The present improved silencer structures has been tested to not exceedan allowable limit of dBA at psi air pressure with a minimum of backpressure within the silencer, in comparison to a similar length ofstandard pipe to which the silencer is attached. Thus, as the airpressure is reduced, the silencer ratings will be proportionatelyreduced. Since most industrial plants specify a pneumatic pressure rangebetween 60 and 80 pounds, several silencers may be working at any oneinterval without producing a sound effect above the acceptable limitsset by the provision of the Walsh-Healy Act, as mentioned above.

While sintered bronze has been referred to in the illustrativeembodiments of the invention, other materials which would be regarded asequivalent thereto include sintered steel, porous porcelain or stone orporous plastic materials.

The present invention may be embodied in certain other forms withoutdeparting from the spirit and essential characteristic thereof,therefore the present embodiment is to be considered illustrative onlyand not restrictive, the scopie of the invention being indicated by theappended claims rather than by the foregoing description.

Having described our invention, reference should now be had to thefollowing claims.

We claim:

1. A silencer comprising a housing having a chamber; a sound absorbingmaterial disposed within said chamber; one end of said housing beingconnected to a source of exhausted air; a first baffle member disposedwithin said housing adjacent said one end; a second baffle memberdisposed within said housing adjacent the other end thereof; said firstand said second baffle members being permeable to permit penetration ofsaid exhausted air through said first bafile member into said chamberand through said sound abosrbing material for exit through said secondbaffle member to the atmosphere; said first baffle member being adaptedto reduce the noise level of said exhausted air to a first value lowerthan the initial entering value; said sound absorbing material withinsaid chamber being adapted to further reduce the noise level of saidexhausted air to a second value lower than said first value; and saidsecond baffle member being adapted to still further reduce the noiselevel of said exhausted air to a third value lower than said first andsecond value;

said first bafile member being formed in the shape of a trun catedcylindrical cone providing an internal gas expansion chamber alignedwith said inlet and said second baffle member being fonned in the shapeof a plate disposed across said other end of said housing.

2. The silencer as defined in claim 1, said first and second bafilemembers being made from sintered bronze.

3. The silencer as defined claim 1, in which said second baffle membercomprises a perforated plate.

4. The silencer as defined in claim 1, wherein the apex of the cone isremote from the inlet to the chamber.

5. The silencer as defined in claim 1, wherein the first baffle memberis of sintered bronze.

6. The silencer as defined in claim 5, wherein the second baffle memberis a perforated plate.

7. The silencer as defined in claim 4, wherein the first baffle memberis of sintered bronze.

1. A silencer comprising a housing having a chamber; a sound absorbingmaterial disposed within said chamber; one end of said housing beingconnected to a source of exhausted air; a first baffle member disposedwithin said housing adjacent said one end; a second baffle memberdisposed within said housing adjacent the other end thereof; said firstand said second baffle members being permeable to permit penetration ofsaid exhausted air through said first baffle member into said chamberand through said sound abosrbing material for exit through said secondbaffle member to the atmosphere; said first baffle member being adaptedto reduce the noise level of said exhausted air to a first valUe lowerthan the initial entering value; said sound absorbing material withinsaid chamber being adapted to further reduce the noise level of saidexhausted air to a second value lower than said first value; and saidsecond baffle member being adapted to still further reduce the noiselevel of said exhausted air to a third value lower than said first andsecond value; said first baffle member being formed in the shape of atruncated cylindrical cone providing an internal gas expansion chamberaligned with said inlet and said second baffle member being formed inthe shape of a plate disposed across said other end of said housing. 2.The silencer as defined in claim 1, said first and second baffle membersbeing made from sintered bronze.
 3. The silencer as defined claim 1, inwhich said second baffle member comprises a perforated plate.
 4. Thesilencer as defined in claim 1, wherein the apex of the cone is remotefrom the inlet to the chamber.
 5. The silencer as defined in claim 1,wherein the first baffle member is of sintered bronze.
 6. The silenceras defined in claim 5, wherein the second baffle member is a perforatedplate.
 7. The silencer as defined in claim 4, wherein the first bafflemember is of sintered bronze.